The long-term objective of this mentored five-year development award is to achieve the independent investigative skills necessary to precisely identify biomechanical factors contributing to musculoskeletal dysfunction of the shoulder, specifically the subacromial impingement syndrome (SIS). The complexity of SIS dictates that a state-of-the-art, multi-faceted approach of exploration will be most effective in leading to an understanding of the pathomechanisms of this common problem. Training will target four scientific domains: anatomical quantification, soft tissue mechanics, movement science, and clinical research application. Each domain will be explored through coursework, mentored laboratory experiences, seminars and conferences, and scholarship. The research plan for this award will investigate the role of the posterior glenohumeral capsule in SIS. Decreased posterior capsule extensibility is believed to contribute to SIS by altering humeral head translations, diminishing the subacromial space, and repetitively compressing the rotator cuff or biceps tendons during arm elevation. The first specific aim of this project is to determine a clinically valid measure of posterior capsule extensibility using strain gauges and an electrogoniometer. The second specific aim is to determine the precise relationship of posterior capsule contracture to SIS. MRI and three-dimensional image reconstruction will be used to quantify the subacromial space before and after modeling posterior capsule extensibility alterations in cadavers. Contact pressures in the subacromial space, humeral head kinematics, and posterior capsule strain will also be measured after altering posterior capsule extensibility. The proposed development plan will result in an independent scientist with a unique set of skills with which to further explore the mechanisms of subacromial impingement and other pathologies of the shoulder joint complex. The research plan will determine the role of posterior capsule extensibility on movement dysfunction and SIS. Findings will be incorporated into the clinical diagnosis of movement dysfunction at the shoulder. Rehabilitation strategies targeting the posterior capsule will then be developed and tested for effectiveness. The findings of this research are likely to improve shoulder rehabilitation, decrease patient impairment and disability, prevent impingement, and lower health care costs.